On the ontology of entities in quantum chemistry

S. FORTIN; J. A. JAIMES ARRIAGA; H. ACCORINTI

Paris

Workshop; Identity in science and philosophy; 2019

Université Paris Diderot

From the successes achieved in physics by applying Quantum Mechanics (MC) to chemical systems in the early twentieth century, the idea that chemistry can be completely reduced to physics, both epistemologically and ontologically, has been disseminated. Although in recent decades, and together with the emergence of the philosophy of chemistry, this fact has been questioned, it remains the predominant position in the scientific-philosophical field. In this work we will analyze in detail the methods used by those who positively apply quantum mechanics to chemical systems.On the one hand, the Born-Oppenheimer approach assumes that since the mass of the atomic nuclei is much greater than that of electrons, then the nuclei can be considered to be still. On the other hand, the orbital approach establishes that in an atom with many electrons the quantum entanglement between them is not important. Based on this assumption, a separate wave function is assigned to each electron.The two approaches mentioned contradict the principles of quantum mechanics. On the one hand, Heisenberg's principle of indeterminacy, together with the Kochen-Specker theorem, states that it is not possible to simultaneously assign defined values ??to the position and velocity of a quantum particle. However, the Born-Oppenheimer approach establishes that the atomic nuclei are still, that is, they have a well defined position and velocity. On the other hand, according to quantum mechanics, a physical system of N particles has a wave function of 3N dimensions associated with it. Since traditional physical space has only 3 dimensions, the space that inhabits the wave function has been the subject of intense debates within the philosophy of physics. However, the orbital approach disregards the holistic multidimensional space of quantum mechanics and states that each of the electrons that form an atom has a three-dimensional wave function and separated from the rest.From this analysis, and from the review of the philosophical literature about approximations, we will argue that the methods used by quantum chemists are not true approximations. We will also develop the idea that the entities that populate the universe of this discipline are ontologically very different from those considered by quantum physics. And for this reason we will move towards our own ontology for quantum chemistry.